This invention relates to apparatus for switching electric current, such as direct current (DC) electricity; and more particularly to such apparatus which has a mechanism for extinguishing arcs formed between switch contacts during separation.
DC electricity is used in a variety of applications such as battery powered systems, drives for motors and DC accessory circuits, in which contactors are used to make and break load current. Weight, reliability and high DC voltage switching and interrupting capability are important considerations in developing the contactor. Furthermore, in many applications relatively large direct currents must be switched which produce arcs when the contacts of the contactor separate, thereby requiring a mechanism for extinguishing the arcs.
Previous DC contactors and switches incorporated one or more arc extinguishing chambers, often referred to as "arc chutes" such as described in U.S. Pat. No. 5,416,455, to extinguish arcs that formed between the switch contacts. Arc extinguishing chambers may comprise a series of spaced apart electrically conductive splitter plates. In DC switching devices, permanent magnets on the sides of the series of splitter plates establish a magnetic field across the arc extinguishing chamber which directs arcs into the splitter plate arrangement. The arc then propagates from one splitter plate to another in the series and eventually the arc spans a number of gaps between the splitter plates whereby sufficient arc voltage is built up that the arc is extinguished.
The arc in DC switching devices can become stabilized in one spot on a given splitter plate. This concentration of energy at one spot erodes the metal plate, particularly when the arc duration is relatively long as occurs with inductive loads.